1. Field of the Invention
The present invention generally pertains to fuse units and their manufacturing method. It further relates to a fuse box, with a fuse cover, adapted to contain the fuse unit. Such a fuse box can be suitably used in vehicles, e.g. automobiles.
2. Description of Background Information
FIG. 1 shows an example of a known fuse box unit which is directly connectable to a battery. A fuse box unit 61 comprises a fuse box 62, flat fuses 63 and other components. The flat fuses 63 are formed by stamping out an electrically conductive metal plate or sheet. Each flat fuse 63 includes a fuse element portion 64 formed in a curved plane and interposed between two ear portions 65 having a respective ear hole for bolting. The fuse element portion 64 is fusible, and its width is set as a function of the current required to be passed. The fuse box 62 is made of a resin, and includes a plurality of enclosures 66 which can contain the corresponding number of flat fuses 63. A pair of flat nuts (first flat nut 67 and second flat nut 68) is insert-molded on the base of each enclosure 66. The first flat nut 67, which is used for power input, has a first flat nut hole for bolting. From this first flat nut 67 extends a terminal directly connectable to a battery (not shown in the figures). Accordingly, a flat fuse 63 is installed and a bolt 69 can be screwed into the ear hole and the first flat nut hole, so that a first end of the flat fuse 63 is connected and fixed to the first flat nut 67 at the power input side. Likewise, the second flat nut 68 has a second flat nut hole for bolting at a power output side. Accordingly, the flat fuse 63 is fixed by screwing down a bolt 69 into the second flat nut hole, so that the other end of the flat fuse 63 is connected to the second flat nut 68 at the power output side.
Electrical cables 71 constituting a wire harness 70 are crimped respectively with an ring terminal 72. These ring terminals 72 are connected and fixed to the second flat nuts 68, together with the flat fuses 63, through the bolts 69. The fuse box 62 is then protected by placing a fuse cover 73 thereon.
However, when a fuse element portion 64 is to be made narrower than a usual size, it tends to curve or bend, and the flat fuse 63 produced therefrom cannot be provided with sufficient mechanical strength. Moreover, it is difficult to manufacture a flat fuse 63 having a small electrical current capacity.
Further, assembling various components into a fuse box unit 61 requires cumbersome work steps, such as a step of fixing a plurality of flat fuses 63 into a fuse box 62 by means of bolts 69 and first and second flat nuts 67 and 68. As a consequence, the prior art fuse box unit has a quite low operation efficiency when mounted.
Furthermore, a prior art fuse box unit 61 must sometimes be constructed by using flat fuses 63 having different current ratings. In such a case, fuse element portions 64 having different widths must be prepared as a function of their current capacity. As a result, several kinds of dies have to be used for stamping, incurring additional production costs.
The present invention was contemplated in the light of the above problems. A first object of the invention is to provide a method of manufacturing a fuse unit in an easy and economical way, irrespective of the current capacity rating required and the number of fuse element portions.
A second object of the invention is to provide a fuse unit which can be manufactured easily at a low cost according to the above method, which fuse unit is endowed with a sufficient mechanical strength and can be fixed easily into a fuse recipient, e.g. a fuse box.
To this end, there is provided a method of forming a fuse unit including an electrically conductive plate having an input terminal, at least one output terminal and at least one fuse element portion linking the input terminal and the at least one output terminals. The fuse unit further includes an insulator material. The method includes stamping the electrically conductive plate so as to form the input terminal and the at least one output terminal, providing at least one locus predetermined for forming the at least one fuse element portion, molding all or part of an area including the at least one locus with the insulator material, and forming the at least one fuse element portion at the at least one locus.
Preferably, the molding includes includes molding a part of the area, such that at least one non-shielded portion is formed for the at least one locus.
Suitably, the molding includes insert-molding a part of the area by means of a die including at least one protrusion, so that the at least one protrusion forms the non-shielded portion.
Preferably yet, the stamping includes stamping the electrically conductive plate so as to form the input terminal, the at least one output terminal having a respective end portion, and at least one tie bar linking the end portions of the at least one output terminal.
Further yet, the forming may include stamping the at least one locus so as to yield the at least one fuse element portion, while simultaneously removing the at least one tie bar by the stamping.
The present invention further relates to a fuse unit including an electrically conductive plate having an input terminal, at least one output terminal and at least one fuse element portion linking the input terminal and the at least one output terminal. The fuse unit further includes an area molded with an insulator material, the area including at least one opening, through which the at least one fuse element portion is exposed to outside the insulator material.
The present invention also concerns a fuse box containing a fuse unit, the fuse unit including an electrically conductive plate having an input terminal, at least one output terminal and at least one fuse element portion linking the at least one input terminal and the at least one output terminal. The fuse unit further includes an area molded with an insulator material, the area including at least one opening, through which the at least one fuse element portion is exposed to outside the insulator material.
The fuse box is configured to have a hollow generally tubular shape having a substantially rectangular cross-section, and a top opening and a bottom opening. The fuse box contains at least one partition wall extending in the longitudinal direction of the tubular shape, thereby forming several enclosures housing the output terminals. The partition walls include a slit extending from the top opening to half-way down in the longitudinal direction, and the slits house the insulator material such that the input terminal extends perpendicularly to the longitudinal direction from the top opening.
The fuse box may further include a fuse cover including a cover plate and a cover joint, the cover plate covering the input terminal of the fuse unit and the cover joint covering the top opening of the fuse box.
In an aspect of the present invention, when the fuse element portion is being built, the peripheral area around it is already reinforced by the insulator material. Accordingly, even when a thin fuse element portion must be formed, the stress, which may cause curving or bending of the fuse element, is minimally exerted towards the fuse element portion. The fuse element portion can thus be rendered less liable to deformation or breaking, and is secured with sufficient strength. Further, even when the fuse element portion must be given a small electrical current rating, it can be formed relatively easily. Further yet, several fuse element portions having a different thickness can be formed using only one kind of die. Costs incurred for die preparation can thus be reduced to minimum, and the fuse units can thus be produced at low cost.
In another aspect of the invention, the end portions of the output terminals are linked to each other by tie bars. By virtue of this configuration, the relative positions of the output terminals are kept constant, up to a time when the fuse element portions are formed by stamping. Further, it is more difficult to exert curving- or bending-inducing stress on the fuse element portion. As a result, the fuse element portion is securely prevented from deformation or breaking.
Further, the tie bars are removed by stamping at the same time the fuse element portion is formed. The number of operation steps, as a whole, can thus be kept to a minimum, leading to improved production efficiency.
When the loci exposing through the window portions are stamped out, the insulator material does not impede the stamping work, which is thus greatly facilitated. In such a case, even when the insulator material used is not sufficiently elastic, the generation of cracks is nonetheless prevented.
In a further aspect of the present invention, as the fuse element portion is exposed through the window portion, the former can be inspected visually, irrespective of the insulator material used. Moreover, such a fuse unit can be constructed easily and economically when the above-mentioned method is applied.